Immunology Graduate Program, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
J Leukoc Biol. 2009 Nov;86(5):1227-38. doi: 10.1189/jlb.0309164. Epub 2009 Aug 12.
CDC are exotoxins secreted by many Gram-positive bacteria that bind cholesterol and oligomerize to form pores in eukaryotic cell membranes. We demonstrate that CDC TLO induces caspase-1 cleavage and the rapid release of IL-1beta from LPS-primed murine BMDM. IL-1beta secretion depends on functional toxin pore formation, as free cholesterol, which prevents TLO binding to cell membranes, blocks the cytokine release. Secretion of the mature forms of IL-1beta and caspase-1 occurs only at lower TLO doses, whereas at a higher concentration, cells release the biologically inactive proforms. IL-1beta release at a low TLO dose requires potassium efflux, calcium influx, and the activities of calcium-independent PLA(2), caspase-1, and cathepsin B. Additionally, mature IL-1beta release induced by a low TLO dose is dependent on the NLRP3 inflammasome, and pro-IL-1beta release induced by a high TLO dose occurs independently of NLRP3. These results further elucidate a mechanism of CDC-induced IL-1beta release and suggest a novel, immune evasion strategy in which IL-1beta-containing macrophages might release primarily inactive cytokine following exposure to high doses of these toxins.
细胞分裂调控蛋白（CDC）是许多革兰氏阳性菌分泌的外毒素，它们可以与胆固醇结合并寡聚化，在真核细胞膜上形成孔道。我们证明，CDC TLO 可诱导 LPS 预刺激的鼠源 BMDM 中 caspase-1 的切割和 IL-1β的快速释放。IL-1β的分泌依赖于功能性毒素孔的形成，因为游离胆固醇可阻止 TLO 与细胞膜结合，从而阻断细胞因子的释放。只有在较低的 TLO 剂量下，才能分泌成熟形式的 IL-1β和 caspase-1，而在较高浓度下，细胞则释放无生物活性的前体形式。在低 TLO 剂量下，IL-1β的释放需要钾离子外流、钙离子内流以及钙非依赖性 PLA2、caspase-1 和组织蛋白酶 B 的活性。此外，低 TLO 剂量诱导的成熟 IL-1β释放依赖于 NLRP3 炎性小体，而高 TLO 剂量诱导的 pro-IL-1β释放则独立于 NLRP3 发生。这些结果进一步阐明了 CDC 诱导的 IL-1β释放的机制，并提出了一种新的免疫逃避策略，即这些毒素暴露于高剂量时，含 IL-1β的巨噬细胞可能主要释放无活性细胞因子。
